We propose to use the selectively stabilized image technique to study the adaptational effects attributable to color separately from those attributable to wavelength. This technique will allow us to stabilize part of the retinal image while leaving the rest unstabilized. The part of the image that is stabilized will disappear and be filled-in by the perceptual characteristics of the adjacent unstabilized retinal image. Thus, by stabilizing only part of the retinal image, we can evoke the filling-in mechanism as a means of changing the color of a background field without changing its wavelength. We can then use this background field to examine whether the color or the wavelength of the background field determines its adaptational effects on other visual stimuli. We will study the effects of color and wavelength on two-color increment thresholds and opponent color equilibria under conditions in which the color of a critical part of the perceptual image is changed drastically by filling-in of a stabilized image. We will attempt to relate the results to current color theory and to show their generality under normal viewing conditions.